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Re: [Discuss-gnuradio] Transmit filtering
From: |
Marcus D. Leech |
Subject: |
Re: [Discuss-gnuradio] Transmit filtering |
Date: |
Mon, 05 Sep 2011 11:46:28 -0400 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 |
On 05/09/11 10:19 AM, John Ackermann N8UR wrote:
> I'm generating two NBFM signals, offsetting them plus and minus 25 kHz
> with FreqXlatingFilters, and combining the output in an adder which
> then drives a USRP sink. It seems sensible to put a bandpass filter
> on the result.
>
> I have a basic conceptual confusion. I would think that you'd specify
> a bandpass filter around zero with a low cutoff of, say, -40e3 and a
> high cutoff of +40e3. However, this doesn't work -- the bandpass
> filter seems to require a number >0 for the lowpass frequency.
Make sure that you specify complex-taps. I assume you're using GRC. By
default, it uses the version of
the bandpass filter with real taps. But if you specify complex taps,
you can use negative frequencies.
--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org